rn-71: add new --diff-merge options article

Author: chriscool

rev_news/drafts/edition-71.md

@@ -21,9 +21,72 @@ This edition covers what happened during the month of December 2020.
 ### General
 -->
 
-<!---
 ### Reviews
--->
+
+*[[PATCH 00/26] git-log: implement new --diff-merge options](https://lore.kernel.org/git/[email protected]/)
+
+ Last November Sergey Organov sent a 26 patch long series to the
+ mailing list. This series added a number of new modes to
+`git log --diff-merges=<mode>`.
+
+ Before this patch series, there would be no diff for merge commits
+ unless one of `-m`, `-c` or `--cc` was given. And in case one of
+ these options was given, then `--diff-merges=off`, or its
+`--no-diff-merges` synonym, could be used to remove that diff output
+ for merge commits. This was the only possible use of
+`--diff-merges=<mode>`.
+
+ Sergey's patch series introduced four new modes. Three of them,
+ "separate", "combined" and "dense-combined" do not generate new diff
+ output. They are just synonyms of `-m`, `-c` and `--cc`
+ respectively.
+
+ The fourth new mode, called "first-parent", though allows to get the
+ same output as `-p --first-parent` but "without the changes in
+ history traversal that the `--first-parent` option causes".
+
+ Sergey's patch series also refactored some code and fixed a small
+ issue. In a follow up email Sergey asked questions related to
+ further possible issues related to how `-m`, `-c` and `--cc`
+ interact with `--oneline`.
+
+ Elijah Newren replied to Sergey's questions, and a long discussion
+ involving Junio Hamano, the Git maintainer, started about different
+ technical topics, especially the interactions between `-p` and the
+`-m`, `-c` and `--cc` options.
+
+ Elijah and Philip Oakley also commented on small issues in a few
+ patches.
+
+ Sergey then sent a new version, that he named v1, of his patch
+ series with 27 patches, so one more than in the original series. The
+ changes were mostly typo and documentation fixes.
+
+ Elijah and Junio commented on the patch series. Elijah and Sergey
+ discussed some new `--remerge-diff` and `--remerge-diff-only`
+ options Elijah had been working on, and how there could also be a
+ related `--diff-merges=remerge` mode.
+
+ Junio found a few issues and suggested some renaming and test
+ improvements.
+
+ Sergey sent a new v2 version of his patch series with 33 patches, so
+ 6 more than in v1. One change compared to the previous version was
+ that the diff output for the new --diff-merges options didn't affect
+ non-merge commits. Another change was that short mnemonics
+`--diff-merges=(1|m|c|cc)` were provided on top of long mode
+ names. A lot of smaller changes addressed Elijah's and Junio's
+ reviews.
+
+ Elijah and Sergey then discussed further improvements especially to
+ the documentation. Felipe Contreras and Junio sometimes also chimed
+ in with further explanations or suggestions.
+
+ Sergey sent a new v3 version, with 32 patches, one less than in v2.
+ The changes were mostly following reviewers' suggestions. Felipe
+ commented positively on one patch, and Junio said he didn't spot
+ anything objectionable in the series and was ok to start merging it
+ to the next branch.
 
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 ### Support